Detecting hemodynamic stability during arrhythmia using the changes in atrial activation

ABSTRACT

Detected changes in atrial activation can be used to discriminate between hemodynamically stable and hemodynamically unstable tachyarrhythmias.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/302,730, filed on Feb. 9, 2010, under 35 U.S.C. §119(e), which isincorporated herein by reference in its entirety.

BACKGROUND

Implantable medical devices (IMDs) are devices designed to be implantedinto a patient. Some examples of these devices include cardiac rhythmmanagement (CRM) devices. CRM devices include implantable pacemakers,implantable cardioverter defibrillators (ICDs), and devices that includea combination of pacing and defibrillation including cardiacresynchronization therapy. The devices are typically used to treatpatients using electrical therapy and to aid a physician or caregiver inpatient diagnosis through internal monitoring of a patient's condition.The devices can include electrical leads in communication with senseamplifiers to monitor electrical heart activity within a patient, andoften include sensors to monitor other internal patient parameters.Other examples of implantable medical devices include implantableinsulin pumps or devices implanted to administer drugs to a patient.

Additionally, some IMDs detect events by monitoring electrical heartactivity signals. By monitoring cardiac signals, IMDs are able to detectabnormally rapid heart rate, or tachyarrhythmia. Although detecting anoccurrence of tachyarrhythmia is important, it can be even more helpfulif additional physiologic information is known about thetachyarrhythmia, such as if the tachyarrhythmia is hemodynamicallystable or unstable. An IMD that can not only detect tachyarrhythmias,but also discriminate between hemodynamically stable and unstabletachyarrhythmias, can be used to help guide therapy decisions.

OVERVIEW

This document describes, among other things, systems and methods fordiscriminating between hemodynamically stable and hemodynamicallyunstable tachyarrhythmias using detected changes in atrial activation.

Example 1 can include subject matter that can include an apparatuscomprising: a cardiac rhythm management device comprising: an atrialactivation sensing circuit configured to sense an atrial activation of asubject; a tachyarrhythmia detection circuit configured to detectwhether tachyarrhythmia is present in a subject; and a processorcircuit, coupled to the atrial activation sensing circuit and thetachyarrhythmia detection circuit, the processor configured to: comparea characteristic of the atrial activation present just before thetachyarrhythmia was detected to a characteristic of the atrialactivation during the detected tachyarrhythmia; and use the comparisonto determine a hemodynamic stability characteristic of thetachyarrhythmia.

In Example 2, the subject matter of Example 1 can optionally include thecharacteristic of the atrial activation including at least one of: anatrial rate or interval, or an atrial or interval variability.

In Example 3, the subject matter of any one of Examples 1-2 canoptionally include the characteristic of the atrial activation beingdetermined over multiple cardiac cycles.

In Example 4, the subject matter of any one of Examples 1-3 canoptionally include the processor configured to: compare an atrial ratepresent just before the tachyarrhythmia was detected to an atrial rateduring the detected tachyarrhythmia; determine that the atrial rateduring the detected tachyarrhythmia is not substantially increased fromthe atrial rate present just before the tachyarrhythmia was detected;and declare that the tachyarrhythmia is hemodynamically stable when itis determined that the atrial rate during the detected tachyarrhythmiais not substantially increased from the atrial rate present just beforethe tachyarrhythmia was detected.

In Example 5, the subject matter of any one of Examples 1-4 canoptionally include the processor configured to: compare an atrial ratepresent just before the tachyarrhythmia was detected to an atrial rateduring the detected tachyarrhythmia; determine that the atrial rateduring the detected tachyarrhythmia is substantially increased from theatrial rate present just before the tachyarrhythmia was detected; anddeclare that the tachyarrhythmia is hemodynamically unstable when it isdetermined that the atrial rate during the detected tachyarrhythmia issubstantially increased from the atrial rate present just before thetachyarrhythmia was detected.

In Example 6, the subject matter of any one of Examples 1-5 canoptionally include the processor configured to: determine a differencebetween an atrial rate variability present just before thetachyarrhythmia was detected to an atrial rate variability during thedetected tachyarrhythmia; compare the difference to a threshold value;when the difference is above the threshold value, declare that thetachyarrhythmia is hemodynamically stable; and when the difference isbelow the threshold value, declare that the tachyarrhythmia ishemodynamically unstable.

In Example 7, the subject matter of any one of Examples 1-6 canoptionally include the processor configured to, in response to adetected tachyarrhythmia, determine whether the sensed atrial rateexceeds a threshold value; and when the sensed atrial rate exceeds thethreshold value, declare the tachyarrhythmia to be hemodynamicallyunstable; and when the sensed atrial rate is less than the thresholdvalue, declare the tachyarrhythmia to be hemodynamically stable.

In Example 8, the subject matter of any one of Examples 1-7 canoptionally include the processor configured to trigger communication anindication of the hemodynamic stability characteristic of thetachyarrhythmia to a user interface or process.

In Example 9, the subject matter of any one of Examples 1-8 canoptionally include a therapy circuit, coupled to the processor, thetherapy circuit configured to provide therapy to the subject; whereinthe processor is configured to use the hemodynamic stabilitycharacteristic of the tachyarrhythmia to control therapy provided to thesubject.

In Example 10, the subject matter of any one of Examples 1-9 canoptionally include the therapy circuit configured to provideanti-tachyarrhythmia pacing to the subject when the tachyarrhythmia ishemodynamically stable.

In Example 11, the subject matter of any one of Examples 1-10 canoptionally include the therapy circuit configured to provide shocktherapy to the subject when the tachyarrhythmia is hemodynamicallyunstable.

In Example 12, the subject matter of any one of Examples 1-11 canoptionally include the therapy circuit configured to withhold shocktherapy when the tachyarrhythmia is hemodynamically stable.

In Example 13, the subject matter of any one of Examples 1-12 canoptionally include a therapy circuit, coupled to the processor, thetherapy circuit configured to deliver therapy to the subject in responseto a detected tachyarrhythmia; wherein the processor is configured to:compare an atrial characteristic present during the tachyarrhythmia andjust before delivery of therapy to an atrial characteristic presentduring or after delivery of therapy; and use the comparison to do atleast one of: 1) confirm or detect a change in the hemodynamic stabilitycharacteristic of the tachyarrhythmia, or 2) adjust the therapy.

Example 14 can include, or can optionally be combined with any one ofExamples 1-13 to include subject matter that can include an apparatuscomprising: a cardiac rhythm management device comprising: an atrialrate sensing circuit configured to sense an atrial rate of a subject; atachyarrhythmia detection circuit configured to detect whethertachyarrhythmia is present in a subject; and a processor circuit,coupled to the atrial rate sensing circuit and the tachyarrhythmiadetection circuit, the processor configured to: detect an atrial ratetrend present at least 5 seconds after the start of the detectedtachyarrhythmia; determine whether the atrial rate trend present atleast 5 seconds after the start of the detected tachyarrhythmia isincreasing or decreasing; and use the determination to declare ahemodynamic stability characteristic of the tachyarrhythmia.

In Example 15, the subject matter of any one of Examples 1-14 canoptionally include the processor circuit configured to declare that thetachyarrhythmia is hemodynamically unstable when it is determined thatthe atrial rate trend present at least 5 seconds after the start of thedetected tachyarrhythmia is increasing.

In Example 16, the subject matter of any one of Examples 1-15 canoptionally include the processor circuit configured to declare that thetachyarrhythmia is hemodynamically stable when it is determined that theatrial rate trend present at least 5 seconds after the start of thedetected tachyarrhythmia is decreasing.

In Example 17, the subject matter of any one of Examples 1-16 canoptionally include the atrial rate trend being determined over multiplecardiac cycles.

In Example 18, the subject matter of any one of Examples 1-17 canoptionally include the processor configured to trigger communication anindication of the hemodynamic stability characteristic of thetachyarrhythmia to a user interface or process.

In Example 19, the subject matter of any one of Examples 1-18 canoptionally include a therapy circuit, coupled to the processor, thetherapy circuit configured to provide therapy to the subject; whereinthe processor is configured to use the hemodynamic stabilitycharacteristic of the tachyarrhythmia to control therapy provided to thesubject.

In Example 20, the subject matter of any one of Examples 1-19 canoptionally include the therapy circuit configured to provideanti-tachyarrhythmia pacing to the subject when the tachyarrhythmia ishemodynamically stable.

In Example 21, the subject matter of any one of Examples 1-20 canoptionally include the therapy circuit configured to provide shocktherapy to the subject when the tachyarrhythmia is hemodynamicallyunstable.

In Example 22, the subject matter of any one of Examples 1-21 canoptionally include the therapy circuit configured to withhold shocktherapy when the tachyarrhythmia is hemodynamically stable.

In Example 23, the subject matter of any one of Examples 1-22 canoptionally include a therapy circuit, coupled to the processor, thetherapy circuit configured to deliver therapy to the subject in responseto a detected tachyarrhythmia; wherein the processor is configured to:compare an atrial rate trend present during the tachyarrhythmia and justbefore delivery of therapy to an atrial rate trend present during orafter delivery of therapy; and use the comparison to do at least oneof: 1) confirm or detect a change in the hemodynamic stabilitycharacteristic of the tachyarrhythmia, or 2) adjust the therapy.

Example 24 can include, or can optionally be combined with any one ofExamples 1-23 to include subject matter that can include sensing anatrial activation of a subject; detecting that a tachyarrhythmia ispresent in the subject; comparing a characteristic of the atrialactivation present just before the tachyarrhythmia was detected to acharacteristic of the atrial activation during the detectedtachyarrhythmia; and using the comparison to determine a hemodynamicstability characteristic of the tachyarrhythmia.

In Example 25, the subject matter of any one of Examples 1-24 canoptionally include the characteristic of the atrial activation includingat least one of: an atrial rate or interval, or an atrial rate orinterval variability.

In Example 26, the subject matter of any one of Examples 1-25 canoptionally include the characteristic of the atrial activation beingdetermined over multiple cardiac cycles.

In Example 27, the subject matter of any one of Examples 1-26 canoptionally include comparing an atrial rate present just before thetachyarrhythmia was detected to an atrial rate during the detectedtachyarrhythmia; determining that the atrial rate during the detectedtachyarrhythmia is not substantially increased from the atrial ratepresent just before the tachyarrhythmia was detected; and declaring thatthe tachyarrhythmia is hemodynamically stable upon determining that theatrial rate during the detected tachyarrhythmia is not substantiallyincreased from the atrial rate present just before the tachyarrhythmiawas detected.

In Example 28, the subject matter of any one of Examples 1-27 canoptionally include comparing an atrial rate present just before thetachyarrhythmia was detected to an atrial rate during the detectedtachyarrhythmia; determining that the atrial rate during the detectedtachyarrhythmia is substantially increased from the atrial rate presentjust before the tachyarrhythmia was detected; and declaring that thetachyarrhythmia is hemodynamically unstable upon determining that theatrial rate during the detected tachyarrhythmia is substantiallyincreased from the atrial rate present just before the tachyarrhythmiawas detected.

In Example 29, the subject matter of any one of Examples 1-28 canoptionally include determining a difference between an atrial ratevariability present just before the tachyarrhythmia was detected to anatrial rate variability during the detected tachyarrhythmia; comparingthe difference to a threshold value; when the difference is above thethreshold value, declaring that the tachyarrhythmia is hemodynamicallystable; and when the difference is below the threshold value, declaringthat the tachyarrhythmia is hemodynamically unstable.

In Example 30, the subject matter of any one of Examples 1-29 canoptionally include: in response to detecting that the tachyarrhythmia ispresent, determining whether the sensed atrial rate exceeds a thresholdvalue; and when the sensed atrial rate exceeds the threshold value,declaring the tachyarrhythmia to be hemodynamically unstable; and whenthe sensed atrial rate is less than the threshold value, declaring thetachyarrhythmia to be hemodynamically stable.

In Example 31, the subject matter of any one of Examples 1-30 canoptionally include communicating an indication of the hemodynamicstability characteristic of the tachyarrhythmia to a user interface orprocess.

In Example 32, the subject matter of any one of Examples 1-31 canoptionally include using the hemodynamic stability characteristic of thetachyarrhythmia to control therapy provided to the subject.

In Example 33, the subject matter of any one of Examples 1-32 canoptionally include providing anti-tachyarrhythmia pacing to the subjectwhen the tachyarrhythmia is hemodynamically stable.

In Example 34, the subject matter of any one of Examples 1-33 canoptionally include providing shock therapy to the subject when thetachyarrhythmia is hemodynamically unstable.

In Example 35, the subject matter of any one of Examples 1-34 canoptionally include withholding shock therapy when the tachyarrhythmia ishemodynamically stable.

In Example 36, the subject matter of any one of Examples 1-35 canoptionally include delivering therapy to the subject in response to adetected tachyarrhythmia; comparing an atrial characteristic presentduring the tachyarrhythmia and just before delivery of therapy to anatrial characteristic present during or after delivery of therapy; andusing the comparison to do at least one of: 1) confirm or detect achange in the hemodynamic stability characteristic of thetachyarrhythmia, or 2) adjust the therapy.

Example 37 can include, or can optionally be combined with any one ofExamples 1-36 to include subject matter that can include sensing anatrial rate of a subject; detecting that a tachyarrhythmia is present inthe subject; detecting an atrial rate trend present at least 5 secondsafter the start of the detected tachyarrhythmia; determining whether theatrial rate trend present at least 5 seconds after the start of thedetected tachyarrhythmia is increasing or decreasing; and using thedetermination to declare a hemodynamic stability characteristic of thetachyarrhythmia.

In Example 38, the subject matter of any one of Examples 1-37 canoptionally include declaring that the tachyarrhythmia is hemodynamicallyunstable upon determining that the atrial rate trend present at least 5seconds after the start of the detected tachyarrhythmia is increasing.

In Example 39, the subject matter of any one of Examples 1-38 canoptionally include declaring that the tachyarrhythmia is hemodynamicallystable upon determining that the atrial rate trend present at least 5seconds after the start of the detected tachyarrhythmia is decreasing.

In Example 40, the subject matter of any one of Examples 1-39 canoptionally include the atrial rate trend being determined over multiplecardiac cycles.

In Example 41, the subject matter of any one of Examples 1-40 canoptionally include communicating an indication of the hemodynamicstability characteristic of the tachyarrhythmia to a user interface orprocess.

In Example 42, the subject matter of any one of Examples 1-41 canoptionally include using the hemodynamic stability characteristic of thetachyarrhythmia to control therapy provided to the subject.

In Example 43, the subject matter of any one of Examples 1-42 canoptionally include providing anti-tachyarrhythmia pacing to the subjectwhen the tachyarrhythmia is hemodynamically stable.

In Example 44, the subject matter of any one of Examples 1-43 canoptionally include providing shock therapy to the subject when thetachyarrhythmia is hemodynamically unstable.

In Example 45, the subject matter of any one of Examples 1-44 canoptionally include withholding shock therapy when the tachyarrhythmia ishemodynamically stable.

In Example 46, the subject matter of any one of Examples 1-45 canoptionally include delivering therapy to the subject in response to adetected tachyarrhythmia; comparing an atrial rate trend present duringthe tachyarrhythmia and just before delivery of therapy to an atrialrate trend present during or after delivery of therapy; and using thecomparison to do at least one of: 1) confirm or detect a change in thehemodynamic stability characteristic of the tachyarrhythmia, or 2)adjust the therapy.

These examples can be combined in any permutation or combination. Thisoverview is intended to provide an overview of subject matter of thepresent patent application. It is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information about the present patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 shows an example of an implantable or other ambulatory cardiacrhythm management (CRM) device.

FIG. 2 shows an example of portions of the CRM device electronics unit.

FIGS. 3A and 3B show examples of experimental animal data demonstratingthe effects of induced tachyarrhythmia on atrial activation and bloodpressure.

FIG. 4 shows an example of experimental animal data demonstrating alinear relationship between blood pressure and atrial interval duringtachyarrhythmia.

FIG. 5 shows examples of experimental animal data demonstratingdifferences in the variability of atrial activation duringhemodynamically stable and unstable tachyarrhythmias.

FIGS. 6A-6C show examples of methods for detecting hemodynamic stabilityduring tachyarrhythmia using changes in atrial activation.

DETAILED DESCRIPTION

The baroreflex, or baroreceptor reflex, is one of the body's homeostaticmechanisms for maintaining blood pressure. It provides a negativefeedback loop in which an elevated blood pressure can reflexively causeblood pressure to decrease. More specifically, elevated blood pressurecan cause an increase in baroreceptor firing rate, which can lead toincreased parasympathetic activity and decreased sympathetic activity.This, in turn, can lead to a decreased firing rate of the sinoatrial(SA) node, decreased cardiac contractility, and increasedvasodilation—all of which can ultimately result in decreased cardiacoutput and decreased blood pressure. Similarly, a decreased bloodpressure can depress the baroreflex, providing a negative feedback loopthat results in increased blood pressure.

The baroreflex can contribute to the recovery of arterial pressureduring hemodynamically stable tachyarrhythmia, which is tachyarrhythmiathat does not cause a significant drop in the patient's blood pressureor cardiac output. Within the first five seconds of onset ofhemodynamically stable tachyarrhythmia, blood pressure can drop 20-30%from baseline due to less efficient pumping of the heart. The lowestblood pressure can occur about 5 to 10 seconds after onset, and then theblood pressure can start to recover, or increase back up towardpre-tachyarrhythmia baseline levels. It is believed that blood pressurerecovery during hemodynamically stable tachyarrhythmia is a result ofincreased sympathetic activity due to decreased firing of thebaroreceptor, which leads to vasoconstriction, increased contractility,and increased firing of the SA node, all of which cause a rise in bloodpressure.

On the other hand, during hemodynamically unstable tachyarrhythmia,sensitivity of the baroreflex can be reduced and the baroreflexmechanism can fail to produce blood pressure recovery. Hemodynamicallyunstable tachyarrhythmia results in a significant drop in a patient'sblood pressure or cardiac output, such that the global or regionalperfusion is not adequate to support normal organ function. Within thefirst five seconds of onset of hemodynamically stable tachyarrhythmia,blood pressure can drop 50-60% from baseline due to ineffective pumpingof the heart. The blood pressure can then remain low and fail torecover, despite an increased baroreceptor firing rate and increasedsympathetic activity (see, e.g., Hegbom et al.). Therefore, thetreatment of hemodynamically unstable tachyarrhythmia generally requiresshock therapy or cardioversion, whereas hemodynamically stabletachyarrhythmia can generally be managed with anti-tachyarrhythmiapacing (ATP).

The present inventors have recognized, among other things, thathemodynamic stability or instability can be detected duringtachyarrhythmia using changes in atrial activation. Changes in atrialactivation, including changes in atrial rate, interval, or rate/intervalvariability, for example, can be reflective of the hemodynamic stabilityof the tachyarrhythmia via the baroreflex mechanism described above.Thus, during hemodynamically stable tachyarrhythmia, an atrial rate thatis not significantly increased from baseline can reflect recovery ofarterial blood pressure. However, during hemodynamically unstabletachyarrhythmia, a significantly increased atrial rate can reflect asignificant decrease in blood pressure due to decreased baroreflexsensitivity or failure of the baroreflex mechanism. Discriminationbetween hemodynamically stable and unstable tachyarrhythmia based onchanges in atrial activation can be useful in guiding treatment of thetachyarrhythmia.

As used throughout this application, and as understood by one ofordinary skill in the art, the terms “atrial rate” and “atrial interval”have an inverse relationship. Thus, a faster atrial rate corresponds toa shorter atrial interval, and a slower atrial rate corresponds to alonger atrial interval.

FIG. 1 shows an example of an implantable or other ambulatory cardiacrhythm management (CRM) device 100. In an example, the CRM device 100can include an electronics unit 102 that can include ahermetically-sealed biocompatible housing 104 and a header 106 extendingtherefrom. The housing 104 can carry a power source and electronics. Theheader 106 can include one or more receptacles, such as for receivingthe proximal ends of intravascular leads 108A-C. In an example, the lead108A can be an intravascular RV lead that can extend from the superiorvena cava (SVC) into the right atrium (RA), and then into the rightventricle (RV). The lead 108A can include an RV apical tip electrode110, a slightly more proximal RV ring electrode 112, a still slightlymore proximal RV shock coil electrode 114, and an even more proximal RAor SVC shock coil electrode 116. The various electrodes can be used fordelivering electrical energy or sensing intrinsic electrical heartsignals. An intravascular CS/LV lead 108C can extend from the SVC intothe RA, through a coronary sinus (CS) into the coronary vasculature,such as near a portion of a left ventricle (LV). In an example, thissecond CS/LV lead 108C can include at least a distal electrode 118 and aproximal electrode 120, from which electrostimulation energies can bedelivered or intrinsic electrical heart signals can be sensed. Anintravascular right atrial (RA) lead 108B can extend from the SVC intothe RA, and can include a distal electrode 119 and a proximal electrode121. Other electrodes (e.g., a housing electrode 105 on the housing 104,a header electrode 107 on the header 106, an epicardial electrode, asubcutaneous electrode located away from the heart, or an electrodelocated elsewhere) or leads can be used.

In an example, an implantable CRM device 100 can include a communicationcircuit, such as to wireless communicate unidirectionally orbidirectionally with an external local interface 121, such as a CRMdevice programmer, repeater, handheld device, or the like. The localinterface 121 can be configured to communicate via a wired or wirelesscomputer or communication network 122 to a remote interface 124, such asa remote computer or server or the like.

FIG. 2 shows an example of portions of the CRM device electronics unit102. In an example, this can include a switching circuit 200, such asfor selectively connecting to the various electrodes such as on theleads 108A-C or elsewhere. An atrial activation sensing circuit 202 canbe selectively coupled to various electrodes by the switching circuit200, and can include sense amplifiers, filter circuits, other circuitssuch as for sensing intrinsic electrical signals, such as intrinsicatrial heart signals. The atrial activation sensing circuit 202 can becoupled to a tachyarrhythmia detection circuit 204. The tachyarrhythmiadetection circuit 204 can be configured to detect tachyarrhythmia in apatient, such as by using heart rate or morphology information from thedepolarizations sensed by the atrial activation sensing circuit 202. Atherapy circuit 206 can be selectively coupled to various electrodes bythe switching circuit 200, and can include pacing energy generationcircuitry (e.g., capacitive, inductive, or other) such as forgenerating, storing, or delivering an electrostimulation, cardioversion,defibrillation, or other energy. In an example, the atrial activationsensing circuit 202, the tachyarrhythmia detection circuit 204, or thetherapy circuit 206 can be coupled to a processor circuit 212. In anexample, the processor 212 can perform instructions, such as for signalprocessing of signals derived by the atrial activation sensing circuit202 or the tachyarrhythmia detection circuit 204, or for controllingoperation of the therapy circuit 206 or other operations of the CRMdevice 100. The processor 212 can also be coupled to or include a memorycircuit 218, such as for storing or retrieving instructions or data, ora communication circuit 220, such as for communicating with the localinterface 121.

FIGS. 3A and 3B show examples of experimental animal data demonstratingthe effects of induced tachyarrhythmia on atrial activation and bloodpressure. FIGS. 3A and 3B contain data from one animal during twoseparately induced tachyarrhythmia episodes. Panels 302A and 302Billustrate right atrial activity in the animal as detected by anelectrogram. Panels 304A and 304B illustrate right ventricular activityas detected by an electrogram. Panels 306A and 306B illustrate aorticpressure. At time intervals 308A and 308B, in panels 304A and 304B,respectively, ventricular pacing spikes represent the induction ofventricular tachyarrhythmia. Corresponding time intervals 309A and 309B,in panels 302A and 304B, respectively, illustrate atrial spikes that arelikely due to artifacts of the ventricular pacing picked up by theatrial sensing electrodes. Vertical lines 310A and 310B represent thetimes at which pacing was terminated and intrinsic tachyarrhythmiabegan. Horizontal line 312 in panels 306A and 306B shows that the dropin aortic pressure is greater in FIG. 3B than in FIG. 3A. In FIG. 3A,mean arterial pressure (MAP) calculated from the aortic pressure signalduring the tachyarrhythmia is 49.7% of the MAP at baseline (e.g., justprior to induction of tachyarrhythmia). In FIG. 3B, however, MAP duringthe tachyarrhythmia is only 33.1% of the MAP at baseline.

The data in FIGS. 3A and 3B illustrate that the amount by which MAPdecreases during tachyarrhythmia (compared to MAP at baseline)corresponds to the amount of change in atrial activation. In FIG. 3A,the atrial P-to-P interval (PPI) is reduced by 7.4% compared tobaseline, whereas in FIG. 3B the atrial PPI is reduce by 13.0% comparedto baseline. Consequently, atrial rate increases more in FIG. 3B, wherethe drop in MAP was larger, as compared to FIG. 3A, where the drop inMAP was smaller. The greater the drop in MAP, the greater the increasein atrial rate (or decrease in atrial PPI). Thus, changes in atrialresponse during tachyarrhythmia can be used instead of, or in additionto, changes in MAP to detect hemodynamic stability or instability. It isbelieved that such a correlation is due to the baroreflex mechanismdescribed above. Accordingly, FIG. 3A represents hemodynamically stabletachyarrhythmia, whereas FIG. 3B represents hemodynamically unstabletachyarrhythmia. In fact, an ATP burst successfully terminated theepisode in FIG. 3A, and the episode in FIG. 3B required a defibrillationshock for termination.

FIG. 4 shows an example of experimental animal data demonstrating alinear relationship between blood pressure and atrial interval duringtachyarrhythmia. This data was obtained from a single animal 14 daysafter an induced myocardial infarction via occlusion of the leftanterior descending coronary artery. Eleven separately inducedventricular tachyarrhythmia episodes are plotted. Normalized atrial PPIdecrease is represented along the x-axis 402. Normalized atrial PPIdecrease was calculated by dividing the difference between the PPI atbaseline (e.g., just prior to tachyarrhythmia induction) and the PPIduring tachyarrhythmia by the PPI at baseline. Normalized MAP isrepresented along the y-axis 404. Normalized MAP was calculated bydividing the MAP during tachyarrhythmia by the MAP at baseline.

The group of induced tachyarrhythmia episodes plotted at 406 can berepresented by averaged data point 407. Likewise, the group of inducedtachyarrhythmia episodes plotted at 408 can be represented by averageddata point 409. The tachyarrhythmia episodes plotted at 406 show amoderate decrease in normalized MAP and a moderate decrease innormalized atrial PPI, which corresponds to a moderate increase inatrial rate. The tachyarrhythmia episodes plotted at 408 show asignificant decrease in normalized MAP and a significant decrease innormalized atrial PPI, which corresponds to a significant increase inatrial rate. This data suggests that the tachyarrhythmia episodesplotted at 406 are likely to be hemodynamically stable and thetachyarrhythmia episodes plotted at 408 are likely to be hemodynamicallyunstable. In fact, the episodes plotted at 406 were terminated by ATPand the episodes plotted at 408 required shock therapy, which tends toconfirm the suggested hemodynamic characterizations. The linearregression line 410 fitted to the plotted tachyarrhythmia episodes hasan R² of 0.7589, suggesting a relatively strong correlation betweenatrial activation and the decrease in MAP during tachyarrhythmia.Moreover, the fact that the tachyarrhythmia episodes plotted at 406(e.g., hemodynamically stable) are well separated from thetachyarrhythmia episodes plotted at 408 (e.g., hemodynamically unstable)demonstrates that changes in atrial activation—either alone or inconjunction with changes in blood pressure—can be used to differentiatehemodynamically stable tachyarrhythmias from hemodynamically unstabletachyarrhythmias.

FIG. 5 shows examples of experimental animal data demonstratingdifferences in the variability of atrial activation duringhemodynamically stable and unstable tachyarrhythmias. The x-axis 502represents atrial interval count, and the y-axis 504 representsnormalized atrial PPI. The lines labeled 506 contain data pointsillustrated as filled triangles. The lines labeled 508 contain datapoints illustrated as filled squares. Lines 506 and 508 show lowvariability of the normalized PPI (or atrial rate) over time. Inaddition, lines 506 and 508 show a relatively constant normalized PPI(or atrial rate) with no recovery over time. The low variability andabsence of recovery suggests that the data used to produce lines 506 and508 came from animals with hemodynamically unstable tachyarrhythmia. Inthese animals, the baroreflex can be less sensitive and unable toappropriately control atrial activation in response to ventriculartachyarrhythmia. However, lines 510, 512, 514, and 516 (illustrated byopen circles, filled diamonds, open diamonds, and filled circles,respectively), demonstrate high variability, as well as gradual recoveryof normalized atrial PPI (or atrial rate). Thus, the data used to formlines 510, 512, 514, and 516 suggests hemodynamically stabletachyarrhythmia. The animals from which this data was obtained can havepreserved baroreflex-mediated control of atrial activation in responseto ventricular tachyarrhythmia.

FIGS. 6A-6C show examples of methods for detecting hemodynamic stabilityduring tachyarrhythmia using changes in atrial activation. FIG. 6Aillustrates an example of a method 600A for differentiating betweenhemodynamically stable and unstable tachyarrhythmia using changes inatrial rate. At 602, cardiac rhythm is detected and monitored, such asby an implantable CRM device. At 604, baseline atrial rate measurements(e.g., atrial rate measurements taken just before tachyarrhythmiadetection) are acquired or updated. In an example, atrial intervalmeasurements can be taken instead of or in addition to atrial ratemeasurements. In an example, atrial rate or interval measurements can betaken over multiple cardiac cycles. At 606, if the detected cardiacrhythm is in the ventricular tachyarrhythmia zone, such as 120 to 200beats per minute (bpm), then at 608, the detected tachyarrhythmia isclassified. The tachyarrhythmia can be classified, for example, viaanalysis of the detected electrophysiological signal. At 610, if thetachyarrhythmia is classified as either ventricular tachyarrhythmia orventricular fibrillation, then the process flows to 612. At 610, if thetachyarrhythmia is not classified as either ventricular tachyarrhythmiaor ventricular fibrillation, then the process flows to 614.

At 606, if the detected cardiac rhythm is in the ventriculartachyarrhythmia zone, then at 616 an atrial rate measurement is acquiredduring the ventricular tachyarrhythmia. Atrial rate can be acquired at616 concurrently with classification of the tachyarrhythmia at 608. At618, it is determined whether the atrial rate during the ventriculartachyarrhythmia is substantially increased from the baseline atrialrate. In an example, at atrial rate during ventricular tachyarrhythmiathat is more than 10% above the baseline atrial rate can be consideredsubstantially increased. In an example, the atrial rate duringventricular tachyarrhythmia can be compared to a specified thresholdvalue, or range of values, instead of or in addition to being comparedto the baseline atrial rate. In an example, the specified thresholdvalue can vary from patient to patient. If the atrial rate duringtachyarrhythmia is not substantially increased from baseline (or is notabove the threshold value), then at 620 the tachyarrhythmia is declaredhemodynamically stable. If the atrial rate during tachyarrhythmia issubstantially increased from baseline (or is above the threshold value),then at 622 the tachyarrhythmia is declared hemodynamically unstable.After the tachyarrhythmia has been declared hemodynamically stable at620 or unstable at 622, the process flows back to 612 and 614. At 612,if the tachyarrhythmia has been declared hemodynamically stable, then at624 anti-tachyarrhythmia pacing (ATP) is provided to the patient. At612, if the tachyarrhythmia has been declared hemodynamically unstable,then at 626 shock therapy is provided to the patient. At 614, if thetachyarrhythmia has been declared hemodynamically stable, then at 628ATP is provided to the patient. At 214, if the tachyarrhythmia has beendeclared hemodynamically unstable, then at 630 cardioversion is providedto the patient.

In an example, the patient's atrial rate measured during tachyarrhythmiaand just prior to delivery of therapy can be compared to the atrial ratemeasured during or after the delivery of therapy. Such a comparison canbe used to confirm or adjust the hemodynamic characterization of thetachyarrhythmia. For example, if ATP therapy is provided to a patientwith declared hemodynamic stability, and the ATP therapy causes adecrease or stabilization of the atrial rate, then hemodynamic stabilitycan be confirmed. If, on the other hand, the ATP therapy does notdecrease or stabilize the atrial rate, then the patient'stachyarrhythmia may have been misclassified, and may actually behemodynamically unstable. In this case, therapy can be changed, such asby stopping ATP and starting shock therapy or cardioversion.

FIG. 6B illustrates an example of a method 600B for differentiatingbetween hemodynamically stable and unstable tachyarrhythmia usingchanges in atrial rate variability. At 602, cardiac rhythm is detectedand monitored, such as by an implantable CRM device. At 632, baselineatrial rate variability measurements (e.g., atrial rate variabilitymeasurements taken just before tachyarrhythmia detection) are acquiredor updated. In an example, atrial interval variability measurements canbe taken instead of or in addition to atrial rate variabilitymeasurements. In an example, atrial rate/interval variabilitymeasurements can be taken over multiple cardiac cycles. At 606, if thedetected cardiac rhythm is in the ventricular tachyarrhythmia zone, suchas 120 to 200 beats per minute (bpm), then at 608, the detectedtachyarrhythmia is classified. The tachyarrhythmia can be classified,for example, via analysis of the detected electrophysiological signal.At 610, if the tachyarrhythmia is classified as either ventriculartachyarrhythmia or ventricular fibrillation, then the process flows to612. At 610, if the tachyarrhythmia is not classified as eitherventricular tachyarrhythmia or ventricular fibrillation, then theprocess flows to 614.

At 606, if the detected cardiac rhythm is in the ventriculartachyarrhythmia zone, then at 634 an atrial rate variability measurementis acquired during the ventricular tachyarrhythmia. The atrial ratevariability measurement can be acquired at 634 concurrently withclassification of the tachyarrhythmia at 608. At 636, the differencebetween atrial rate variability during the tachyarrhythmia and theatrial rate variability at baseline is determined. At 638, thedifference is compared to a threshold value. At 638, if the differenceis not above the threshold value, then at 622 the tachyarrhythmia isdeclared hemodynamically unstable. At 638, if the difference is abovethe threshold value, then at 620 the tachyarrhythmia is declaredhemodynamically stable. After the tachyarrhythmia has been declaredhemodynamically stable at 620 or unstable at 622, the process flows backto 612 and 614. At 612, if the tachyarrhythmia has been declaredhemodynamically stable, then at 624 anti-tachyarrhythmia pacing (ATP) isprovided to the patient. At 612, if the tachyarrhythmia has beendeclared hemodynamically unstable, then at 626 shock therapy is providedto the patient. At 614, if the tachyarrhythmia has been declaredhemodynamically stable, then at 628 ATP is provided to the patient. At214, if the tachyarrhythmia has been declared hemodynamically unstable,then at 630 cardioversion is provided to the patient. As described abovewith respect to FIG. 6A, the patient's atrial rate variability beforetherapy can be compared to the atrial rate variability after therapy inorder to confirm or adjust the hemodynamic stability characterization ofthe tachyarrhythmia and to adjust therapy as needed.

FIG. 6C illustrates an example of a method 600C for differentiatingbetween hemodynamically stable and unstable tachyarrhythmia usingchanges in the atrial rate trend present at least 5 seconds after theonset of tachyarrhythmia. At 602, cardiac rhythm is detected andmonitored, such as by an implantable CRM device. At 604, baseline atrialrate measurements (e.g., atrial rate measurements taken just beforetachyarrhythmia detection) are acquired or updated. In an example,atrial interval measurements can be taken instead of or in addition toatrial rate measurements. In an example, atrial rate or intervalmeasurements can be taken over multiple cardiac cycles. At 606, if thedetected cardiac rhythm is in the ventricular tachyarrhythmia zone, suchas 120 to 200 beats per minute (bpm), then at 608, the detectedtachyarrhythmia is classified. The tachyarrhythmia can be classified,for example, via analysis of the detected electrophysiological signal.At 610, if the tachyarrhythmia is classified as either ventriculartachyarrhythmia or ventricular fibrillation, then the process flows to612. At 610, if the tachyarrhythmia is not classified as eitherventricular tachyarrhythmia or ventricular fibrillation, then theprocess flows to 614.

At 606, if the detected cardiac rhythm is in the ventriculartachyarrhythmia zone, then at 640 an atrial rate trend is detected atleast 5 seconds after the onset of the ventricular tachyarrhythmia. Theatrial rate trend can be detected at 640 concurrently withclassification of the tachyarrhythmia at 608. At 642, it is determinedwhether the atrial rate trend at least 5 seconds after ventriculartachyarrhythmia onset is increasing or decreasing. If the atrial ratetrend 5 seconds after tachyarrhythmia onset is decreasing, then at 620the tachyarrhythmia is declared hemodynamically stable. If the atrialrate trend 5 seconds after tachyarrhythmia onset is increasing, then at622 the tachyarrhythmia is declared hemodynamically unstable. After thetachyarrhythmia has been declared hemodynamically stable at 620 orunstable at 622, the process flows back to 612 and 614. At 612, if thetachyarrhythmia has been declared hemodynamically stable, then at 624anti-tachyarrhythmia pacing (ATP) is provided to the patient. At 612, ifthe tachyarrhythmia has been declared hemodynamically unstable, then at626 shock therapy is provided to the patient. At 614, if thetachyarrhythmia has been declared hemodynamically stable, then at 628ATP is provided to the patient. At 214, if the tachyarrhythmia has beendeclared hemodynamically unstable, then at 630 cardioversion is providedto the patient. As described above with respect to FIG. 6A, thepatient's atrial rate variability before therapy can be compared to theatrial rate variability after therapy in order to confirm or adjust thehemodynamic stability characterization of the tachyarrhythmia and toadjust therapy as needed.

Additional Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

All publications, patents, and patent documents referred to in thisdocument are incorporated by reference herein in their entirety, asthough individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. An apparatus comprising: a cardiac rhythm management devicecomprising: an atrial activation sensing circuit configured to sense anatrial activation of a subject; a tachyarrhythmia detection circuitconfigured to detect whether tachyarrhythmia is present in a subject;and a processor, coupled to the atrial activation sensing circuit andthe tachyarrhythmia detection circuit, the processor configured to:compare a characteristic of the atrial activation present just beforethe tachyarrhythmia was detected to a characteristic of the atrialactivation during the detected tachyarrhythmia, wherein thecharacteristic of the atrial activation includes an atrial rate;determine whether the atrial rate during the detected tachyarrhythmia isincreased from the atrial rate present just before the tachyarrhythmiawas detected; and use the comparison to determine a hemodynamicstability characteristic of the tachyarrhythmia, including: declaringthat the tachyarrhythmia is hemodynamically unstable when it isdetermined that the atrial rate during the detected tachyarrhythmia isincreased from the atrial rate present just before the tachyarrhythmiawas detected; and declaring that the tachyarrhythmia is hemodynamicallystable when it is determined that the atrial rate during the detectedtachyarrhythmia is not increased from the atrial rate present justbefore the tachyarrhythmia was detected.
 2. The apparatus of claim 1,wherein the characteristic of the atrial activation includes an atrialrate or interval variability.
 3. The apparatus of claim 1, wherein theprocessor is configured to: determine a difference between an atrialrate variability present just before the tachyarrhythmia was detected toan atrial rate variability during the detected tachyarrhythmia; comparethe difference to a threshold value; when the difference is above thethreshold value, declare that the tachyarrhythmia is hemodynamicallystable; and when the difference is below the threshold value, declarethat the tachyarrhythmia is hemodynamically unstable.
 4. The apparatusof claim 1, comprising a therapy circuit, coupled to the processor, thetherapy circuit configured to provide therapy to the subject; andwherein the processor is configured to use the hemodynamic stabilitycharacteristic of the tachyarrhythmia to control therapy provided to thesubject.
 5. The apparatus of claim 4, wherein the therapy circuit isconfigured to provide anti-tachyarrhythmia pacing to the subject whenthe tachyarrhythmia is hemodynamically stable.
 6. The apparatus of claim4, wherein the therapy circuit is configured to provide shock therapy tothe subject when the tachyarrhythmia is hemodynamically unstable; andwherein the therapy circuit is configured to withhold shock therapy whenthe tachyarrhythmia is hemodynamically stable.
 7. The apparatus of claim4, wherein the therapy circuit is configured to deliver therapy to thesubject in response to a detected tachyarrhythmia, wherein the processoris configured to: compare an atrial characteristic present during thetachyarrhythmia and just before delivery of therapy to an atrialcharacteristic present during or after delivery of therapy; and use thecomparison to do at least one of: confirm or detect a change in thehemodynamic stability characteristic of the tachyarrhythmia, or adjustthe therapy.
 8. The apparatus of claim 1, wherein the characteristic ofthe atrial activation is determined over multiple cardiac cycles.
 9. Theapparatus of claim 1, wherein the processor is configured to triggercommunication of an indication of the hemodynamic stabilitycharacteristic of the tachyarrhythmia to a user interface or process.10. The apparatus of claim 1, wherein the atrial activation sensingcircuit includes an atrial rate sensing circuit configured to sense anatrial rate of a subject, wherein the processor is configured to: detectan atrial rate trend present at least 5 seconds after the start of thedetected tachyarrhythmia; determine whether the atrial rate trendpresent at least 5 seconds after the start of the detectedtachyarrhythmia is increasing or decreasing; and use the determinationto declare a hemodynamic stability characteristic of thetachyarrhythmia.
 11. The apparatus of claim 10, wherein the processor isconfigured to declare that the tachyarrhythmia is hemodynamicallyunstable when it is determined that the atrial rate trend present atleast 5 seconds after the start of the detected tachyarrhythmia isincreasing; and wherein the processor is configured to declare that thetachyarrhythmia is hemodynamically stable when it is determined that theatrial rate trend present at least 5 seconds after the start of thedetected tachyarrhythmia is decreasing.
 12. The apparatus of claim 10,comprising a therapy circuit, coupled to the processor, the therapycircuit configured to provide therapy to the subject; wherein theprocessor is configured to use the hemodynamic stability characteristicof the tachyarrhythmia to control therapy provided to the subject;wherein the therapy circuit is configured to provideanti-tachyarrhythmia pacing to the subject when the tachyarrhythmia ishemodynamically stable; wherein the therapy circuit is configured toprovide shock therapy to the subject when the tachyarrhythmia ishemodynamically unstable; and wherein the therapy circuit is configuredto withhold shock therapy when the tachyarrhythmia is hemodynamicallystable.
 13. The apparatus of claim 10, wherein the atrial rate trend isdetermined over multiple cardiac cycles.
 14. The apparatus of claim 10,wherein the processor is configured to trigger communication anindication of the hemodynamic stability characteristic of thetachyarrhythmia to a user interface or process.